From the
upper contact arc, two whitish arcs run that intersect at the
anthelion. When the sun is high, the arcs extend beyond the anthelion back to the
infralateral arc, creating a kind of loop.
Wegener's counter-sun arc is caused by nearly ideally
horizontally oriented column crystals. The arc becomes indistinct as soon as the crystals deviate slightly from the horizontal position. Therefore, it is very rarely seen. The light rays enter a prism face, are reflected at the base face, and exit the crystal at the next but one prism face.
